12/15/2020
Another couples project nearing finalization. BMW S55 crank hub in both one-piece design and two-piece design.
BMW I6 engines have been plagued with crankshaft flex on their longer stroke engines for decades that shows their head when the power is turned up; the S55 is no exception. The S52 sheared off oil pump shafts at high rpm, and the S54 can't keep OEM dampers together on the track. BMW's management and bean counters manage to ruin an otherwise near flawless S55 engine platform to save machining cost and ease of assembly.
The crank hub sandwiches the keyless oil pump gear and the timing gear to the crank and secures them from rotating by the clamping load from the crank bolt. The crank hub, timing gear, and oil pump gears are separated by 0.006" thick diamond impregnated friction washer. The friction bite system is more that sufficient for holding the oil pump and timing gears, but it is also responsible for transmitting the damping forces of the harmonic damper....this is where failure comes into play.
The harmonic damper on BMW I6 engines have a lot of work do do on these long crank undersquare engines where the power levels have been turned up. This combined with lightning fast shifts from the DTC (dual clutch transmission) creates torsional forces that are at the limit of what the friction bit system can hold. Once that system is torsionally overloaded and the damper's inertia overcomes the friction bite it spins and the timing gear is along for the ride.
We have a solution to positively secure the crank hub, timing gear, and oil pump gear to the crankshaft. Our gears were designed with input from BMW's OEM chain supplier and we followed their design guidelines for gear geometry and surface hardening specs. A lot of time was taken when designing the interlocking mechanisms between the crank hub, oil pump gear, and the crankshaft so new failure points are not introduced into the system. This design will also have one of the highest shear value that maximizes torsional loads transferred through the crank hub to the harmonic damper without failure.
Other designs out there have solid positive interlocking mechanisms, but they have geometry that could fatigue crack given enough time and loading. There are Eastern European budget products out the using Russian TOCT 4543 steel without any surface hardening to keep the product cheap. TOCT 4543 has a hardness of about 29 HRC and will be worn by the much harder timing chain and fuel pump chain.
We aren't first to market, nor are we aren't even a close second, but we will have one of the most well thought out quality designs on the market when it hits!
